Hesiocaeca hessleri (family Hesionidae) is newly described from hydrothermal vents at the Mariana back-arc basin and is only the second species to be described in this deep-sea genus. The new species is most closely related to North Atlantic congeners rather than species from the eastern Pacific. Descriptive comments are provided on two additional polychaetes,
Nicomache arwidssoni (family Maldanidae) and
Amphisamytha galapagensis (family Ampharetidae), that have also been found at this site.